1Hokkaido Kushiro Fisheries Experimental Station, Kushiro, Hokkaido 085-0027, 2Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 3Hokkaido Industrial Technology Center, Hakodate, Hokkaido 041-0801, Japan
Izushi was prepared from raw and salted chum salmon (Oncorhynchus keta) fillets. Effects of salting on the chemical and microbiological characteristics during pre-treatment and the ripening process were investigated to compare these Izushi products. Both reached an acceptable state by ripening for 36 d. During the ripening process, pH values of both Izushi samples remained below pH 5.2 and organic acids in Izushi were mostly acetic acid used as vinegar. By the salting and soaking processes, lower molecular compounds were eluted away and salting decreased microbial counts in Izushi products. In Izushi prepared from salted fish, free amino acids were increased while the increase of VB-N was suppressed during the ripening process, and the fish meat in the ripened product had a more fragile texture. The salting of fish fillets was suggested not to affect microbial flora of Izushi. Regardless of the salting, microbial counts of Izushi did not significantly increase during the ripening process, and after ripening for 36 d or longer, Leuconostoc mesenteroides subsp. cremoris and Saccharomyces cerevisiae became dominant as the groups of lactic acid bacteria and yeasts, respectively.